This project is based upon the premise that the homeostasis of Ca2+ ion concentrations in neuronal tissue may be perturbed in old-age, and that this perturbation may underlie the decreased production and release of the neurotransmitter acetylcholine which has been described in old-age. We have further suggested that a decreased activation of the enzyme pyruvate dehydrogenase by Ca2+ ion may occur upon depolarization of nerve-terminals from aged animals, and that this may be responsible for decreased production of acetyl-CoA, and thence acetylcholine. Using rat synaptosomes (pinched-off presynaptic nerve endings from cerebral cortex) as a model, we have demonstrated decreased acetylcholine synthesis and release in response to KC1-incuced depolarization in old-age. We have also completed a study in which concentrations of cytosolic free Ca2+ were measured with the fluorescent chelating agent Quin-2, in response to plasma membrane depolarization. Further, we have studied the degree of activation of pyruvate dehydrogenase, by covalent modification, in response to membrane depolarization and to inhibitors of mitochondrial Ca2+ transport. These latter two studies were conducted using young adult rats, and we are currently in the process of extending them to senescent animals, in order to answer the questions posed above.